Voltage drops under load

[slowworm]

Do we have any electricians in the homestead? Our house electric supply has always been rather erratic and we finally had the power company install a monitoring device that has recorded the power exceeds the maximum allowed. It also seems to confirm the monitoring device we have is accurate to the nearest volt.

What we have also discovered is that even when the supply is 250v if we have a few devices on such as a kettle, washing machine and oven it can drop to under 210v so we have no doubt in the colder weather it'll go much lower.

Now, the power company have said they can do some things help fix the supply but, being realistic, I think we are always going to have problems so would like to understand what is going on and what we should do. The house is due for a re-wire and one thing that has been suggested is using thicker cable for circuits to reduce any voltage drop in the house.

What I'm after is further advice on how to cope with such a situation. When I try and look into it there seems to be much argument about whos fault it is and rather less advice on what can be done to sort out or mitigate the problems.

 

[ManFriday4]

Where on the system is the monitor unit? Is it at the point where supply enters the building or on the internal wiring?

 

[Broch]

How long are the wire runs in the house? If the cable that was used was based on much lower power devices, especially the ones furthest from the mains input, there will be a voltage drop. However, the problem may be with the gauge of wire delivering the supply to the house; proving that may be difficult.

Our house is an old barn and is long and narrow with the power coming in at one end. When the washing machine switches on in the kitchen at the opposite end, or even worse, the water pump switches in down the borehole, the lights dim; we've just got used to it.

 

[ManFriday4]

Thickness of the copper in the cable is what will influence this.

In my home the sockets downstairs where the expectation of higher loads are- cooker, washing machine tumble dryer lawnmower are on a ring main upstairs they all spurs.

Cable calculators are useful for working out where your problems might be.

Voltage Drop Calculator

www.tlc-direct.co.uk

 

[slowworm]

The power company monitoring unit was installed on the main fuse. Our monitor is on a cocker socket so only about 2m of at least 6mm of cable from the meter.

The problem is not our house wiring, the voltage drop occurs at the point of entry, so this is not a normal long runs of thin house wiring question. (Using a high power electric log splitter I'm aware of voltage drops over cable length and sourced a special extension lead for it).

 

[slowworm]

However, the problem may be with the gauge of wire delivering the supply to the house; proving that may be difficult.

They've already suggested this is the case and we may well get our house supply updated (it's a few hundred meters run). If that happens I expect we will still have some voltage drop due to the length of run and that's what I need to consider.

Currently it drops by about 5-10 volts per 10A drain.

 

[Broch]

I can't remember the figure, but on a nominal 240v supply I thought you were guaranteed (whatever that means) a voltage of at least 'x'. But, that may be unloaded

Whereas changing the house wiring will help a little, especially for the distant loads, it will not solve the problem.

Sorry, I missed one point you made. What do you mean 'the power exceeds the maximum allowed'? Kettle + Washing machine + Oven is likely to be between 5 and 10 kw depending on how modern they are. Our supply is rated at 30kw but, I believe, typical is 23kw (100A supply). Check your main breaker - 60A will only be around 14.5kw; 80A 19kw.

 

[Broch]

Just checked, the recommended max voltage drop at supply is 4%, but that varies depending on the supplier. I think you have grounds to insist on them upgrading the supply.

 

[slowworm]

I mean the voltage of the power supply exceeds the max, which is about 253v and we've had 260v. Min is 216v and we've had it drop to 205v from about 250v. Total kW would have been less than 15 and fuse has been upgraded to 80A.

At the moment I'm not that worried about the max kW we use (that would change if we got an EV) but I am concerned that in winter our max voltage will drop to something like 230v so even a kettle and toaster used at the same time could drop the voltage under 216v.

 

[ManFriday4]

The power company monitoring unit was installed on the main fuse. Our monitor is on a cocker socket so only about 2m of at least 6mm of cable from the meter.

The problem is not our house wiring, the voltage drop occurs at the point of entry, so this is not a normal long runs of thin house wiring question. (Using a high power electric log splitter I'm aware of voltage drops over cable length and sourced a special extension lead for it).

OK this sounds like a to the house delivery issue.

Do you know whether the power company pimut that cable is or was it the house builder?

 

[slowworm]

OK this sounds like a to the house delivery issue.

I know it's a delivery issue. Our power supply is old, overhead cables, installed and owned by the power company.

As said, due to the run to our house if the overhead cables are uprated I still expect a drop in the voltage when things like kettles are used. So over speccing the house wiring would reduce voltage drop within the house, keeping cable runs short and perhaps using a spur circuit rather than a ring for some rooms.

Anything else I need to consider or do?

 

[Broch]

If the unloaded supply is 253v and that drops to 210, with only a few kw devices, then there is a serious supply cable problem as you said. How far away is the nearest transformer? We have a 415 to 240v transformer just 20m from the house - great, that limits the voltage drop; bad, it buzzes in hot weather

I don't believe there is anything you can do that will stop the voltage drop at the supply TBH.

 

[ManFriday4]

Other than maybe limiting running several high load items together.

 

[Great egret]

Over here in the Netherlands you can ask the power company to install a 2 phase configuration in your house, the voltage goes up to 380v in that case. In your case you could regulate 2 phases/380v back to 250v in your house and have a more stable voltage.

 

[Broch]

Err... do you mean 3 phase? our standard supply is '2 phase'.

Getting a 3 phase supply to a domestic premises is a chargeable service in the UK and over a few hundred metres I don't expect it will be cheap.

 

[MikeeMiracle]

250V seems on the high side, the official supply is 230V +10% or -6%. It used to be 240V +6% or -6% but was changed in 1995 to bring us in line with other countries. If your measuring 260V then your outside the tolerance of the supply. It shouldn't create the issue your describing but I would still query that with the supply company.

 

[Great egret]

Err... do you mean 3 phase? our standard supply is '2 phase'.

Getting a 3 phase supply to a domestic premises is a chargeable service in the UK and over a few hundred metres I don't expect it will be cheap.

yes 3 phases offcourse

 

[Hammock_man]

One way to boost the lower levels is to boost the higher off load levels way too high. 240 plus 10% is 264 so you are at the high end for sure. The reason the volts drop is they are being "lost" in the high resistance of the suppy. Chase your supplier.

 

[slowworm]

The upper limit is 230 + 10%, so 253v. As said a few times to network provider are aware and may make changes but being realistic things might improve but I still expect.problems.

I could just put up with it as I do now, so don't use any other high loads if I'm using the electric log splitter, but I'm also looking for other solutions. For example, I notice you can get voltage stabilisers and no doubt there are other solutions out there.